Gas liquefactions by multiple expansion refrigeration



July 1965 u. c. GROSSMANN GAS LIQUEFACTIONS BY MULTIPLE EXPANSION REFRIGERATION Filed Jan. 14, 1963 NITROGEN METHANE INVENTOR. U.C. GROSSMANN A T TORNE K5 United States Patent 3,194,025 GAS LIQUEFACTlQNS BY MULTWLE EXlANdlON REFRIGERATION Ugo C. Grossmann, Seuzach, Zurich, Switzerland, as-

signor to Phillips Petroleum Company, a corporation of Delaware Filed Jan. 14, 1963, Ser. No. 251,265 4 Claims. (Cl. 62-9) This invention relates to a refrigeration system which can be used in lowering the temperature of a material such as in the liquefaction of a gas. In a further aspect, it relates to an improved process and apparatus for liquefying methane or a gas comprising principally methane.

A number of different processes and means have been proposed, patented, or used heretofore for the liquefaction of a gaseous stream of methane, the principal constituent in natural gas. The liquefaction of methane is becoming increasingly important because liquid transport of methane is especially advantageous when the route between the gas source and the point of consumption is mostly by sea or passes through several countries. Large quantities of methane can be stored more economically as liquid than in almost any other way. However, because liquefaction of methane requires removal of heat over a wide temperature range, many of the prior art procedures are uneconomical and inefficient, requiring a number of different refrigerants which are usually caused to go through phase changes, while others require compression and expansion of the methane itself.

Accordingly, this invention provides in its preferred aspects a refrigeration system whereby a gas, particularly one comprising principally methane, or other low boiling gas, is liquefied by removing all heat from the gas, namely the sensible heat and the latent heat of evaporation, which heat is transferred without compression or expansion of the gas itself to a single external or auxiliary refrigerant, such as nitrogen, or helium, in novel indirect heat exchange steps, the refrigerant being made available at lower pressures and temperatures in a closed gas cycle or system. In its broader aspects, this invention provides a novel refrigeration system which can be used to lower the temperature of a material.

Further objects and advantages of this invention will become apparent to those skilled in the art from the following discussion, appended claims, and accompanying drawing in which the single figure schematically illustrates in the form of a flow diagram the preferred embodiment of this invention. In the following description of the drawing and the example to follow, the invention will be illustrated as applied to the liquefaction of methane using gaseous nitrogen as the refrigerant, but the invention is not to be construed in its broader aspects as limited thereto.

Referring now to the drawing, a gaseous process stream 1 comprising methane, is passed through a first plurality of indirect heat exchangers 2, 3 and 4 connected in series to remove the sensible heat from the process stream, and is then passed to a second plurality of indirect heat exchangers ti, 7 and 8 connected in series for the removal of the latent heat of evaporation, so as to produce, as the product of the process, a liquid methane stream ll, which can be passed to a suitable storage vessel or surge tank 11 from which it can be removed via line 12 for use or shipment.

Te heat exchangers shown in the drawing are only illustrated in a schematic fashion, since this invention is not limited to any particular type or configuration of heat exchanger. The type of heat exchanger used will depend upon the material being refrigerated or cooled, the range of temperatures over which the refrigeration must be effected, and other factors which will be apparent to those skilled in the art. Where a gas such as methane is being liquefied, extended surface heat transfer equipment can be used, such as that described in Bulletin IDS-378 (1958) of The Trane Company, LaCrosse, Wisconsin.

The removal of the sensible heat and latent heat of evaporation from the process stream (methane) is accomplished by a closed gaseous refrigerated cycle, such as a nitrogen cycle. The refrigerant is made available at lower pressures and temperatures. Describing this cycle now, the nitrogen gas, e.g. at ambient temperature and low pressure such as 15 p.s.i.a., is initially passed via line 13 to a plurality of alternate compression and cooling zones where it is compressed and cooled. For example, the nitrogen stream 13 is compressed by compressor 14, cooled by cooler 16, compressed further by compressor 1'7, and additionally cooled by cooler 20, to yield a compressed, cooled nitrogen stream 18 having, for example, a pressure of about p.s.i.a. and ambient temperature. The temperature of the initial nitrogen stream 13 is lower than that of process stream 1; the larger the difference in temperature between these two streams, the greater will be the cost of lowering the temperature of the refrigerant, and the smaller the difference in temperature, the greater the amount of heat transfer surface needed. Thus, there will be a balance between these factors so as to make the operation economical. The nitrogen is compressed and cooled to the extent necessary to give the required low refrigerant temperature upon expansion of the compressed stream. The fraction of the compressed refrigerant that is expanded going through each expansion means will depend upon the degree of refrigeration needed at the particular temperature levels. The cooling step following the compression step removes the heat that the nitrogen strearn picks up in the downstream refrigeration steps. The coolant used in coolers l6, 2% can be available cooling water or these coolers can be air-fan coolers, or if even lower temperatures are required, coolants such as liquid propane or liquid ammonia can be used in coolers 16, 26.

The compressed nitrogen stream 18 is divided into two parts, one part being passed via line 19 to the first heat exchanger 2 in a first plurality of heat exchangers and the second part passed via line 21 to expansion means schematically illustrated in the form of a simple expansion valve 22, though such expansion means are preferably expansion turbines or expansion engines. Expansion of stream 21 results, of course, in cooling the stream to a significantly lower temperature, for example F, and in reducing the pressure, preferably to the initial pressure, e.g., l5 p.s.i.a. This cooled expanded stream 23 is then passed through heat exchanger 2 to remove a significant amount of the sensible heat of the process stream 1 and to cool that part of the initially compressed nitrogen stream 19 which is also passed through exchanger 2. Stream 23 can be united with refrigerant stream 24 withdrawn from a subsequent heat exchanger or, as shown in the drawing, can be passed through heat exchanger 2 as a separate stream and after its withdrawal from the heat exchanger united with the initial nitrogen stream 13.

The heat exchange step occurring in heat exchanger 2 can be repeated one or more times until the sensible heat of the process material has been removed therefrom with refrigerant at successively lower temperatures and the refrigerant has a temperature low enough to thereafter remove the latent heat of evaporation of the process material and liquefy the same.

Referring again to the drawing, the cooled refrigerant stream 26 withdrawn from the first heat exchanger 2 is similarly divided into two portions, the first portion 27 being further cooled by passing it through heat exchanger 3, and the second portion being passed via line 28 and expanded by means 29 to an even lower temperature, for example 240 F. and the initial low pressure, e.g., 15 p.s.i.a. The expanded, cooled nitrogen stream 31 is then O similarly passed through heat exchanger 3, again either by combining it with a refrigerant stream 32 withdrawn from a subsequent heat exchanger 4, or passed separately through heat exchanger 3 and thereafter joined with refrigerant stream 24. This second heat exchange step in heat exchanger?) removes further-sensible heat from the process stream 1 and further cools the refrigerant stream 27. The heat exchange step can again be repeated, the refrigerant stream withdrawn via line 33 'being divided into two parts, the first of which is passed via line 34 through heat exchanger 4 for further cooling and the other part passed via line 36 to expansionmeans 37 where itis further cooled, for exampleto '300'F. at p.s.i.a.,

this expanded stream being exchanger 4.

The process stream 39 withdrawn from the last heat exchanger 4 in the first plurality of heat exchangers will be at its dew point, for example -259 F., and it is then liquefied by passing through one or more other heat exchangers. For example, stream 39 is successively passed through a second plurality of heat exchangers 6, 7 and 8. The cooled refrigerant stream 41 withdrawn from the last heat exchanger 4 of the first plurality of heat exchangers is passed to expansion means 42 where his expanded and cooled and then passed via line 43 to heat exchanger 8 for indirect heat exchange with the process material, which is finally withdrawn as liquid Via line 9. This latter heat exchange step can be repeated passed via line 38 to heat upstream a plurality of times, the number of such steps being such that in the last of these steps all the latent heat of evaporation from the process material has been removed and it is produced in its liquid state. For example, the refrigerant withdrawn from heat exchanger is passed via line 44, expanded and cooled by expansion means 46, passed through the heat exchanger-7, withdrawn from the latter via line 47 and similarly expanded by means 48, and then passed through the first or upstream heat exchanger 6, from which it is withdrawn via line 49 and passed successively through the heat exchangers 4, 3 and 2 of the first plurality of heat exchangers as described hereinbefore.

which it is withdrawn with an enthalpy of 184B.t.u./lb. and combined with stream 24. The cooled process stream is withdrawn from heat exchanger 2 at a temperature of 33 F. and an enthalpy of 352 B.t.u./lb., and it is passed to the second heat exchanger 3. The cooled refrigerant withdrawn via line 26 is passed in part at 33 F. to the second heat exchanger 3 via line 27 and the other part, with-an enthalpy of 157 B.t.u./lb., is passed via line 28 at 1.2 lb./unit time to expansion means 29. The expanded nitrogen stream 31 'is passed to the second heat exchanger 3 at 240 F., 15 p.s.i.a., an enthalpy of 107 B.t.u./lb., this latter stream being withdrawn from heat exchanger 3 with an enthalpy of 155 B.t.u./lb. and combined with the refrigerant in line 32 having a temperature of 44 F. 'The. cooled process stream withdrawn from the second heat exchanger 3 has a temperature of 146 F. and an enthalpy of 294 B.t.u./lb. and

Since the refrigerant in the cycle. is in the gas phase throughout, the process can be readily controlled and operated. And the refrigerant cycle used is a closed system, thereby minimizing any fouling;

Further objects and advantages of this invention will become apparent from the following example, and it should be understood that the various pressures, temperatures, number ofheat exchange steps, compression steps, expansion steps, etc. recited in this example are only typical of the preferred embodiment and should not be con strued to limit this invention unduly.

Example Referring to the drawing again, methane, having a specific heat of 0.513 B.t.u./lb./ F. anda latent heat of evaporation of 218 'B.t.u./lb., is supplied by process stream 1 at 80 F. and 30 p.s.i.a., and at a rate of lib/unit time. This stream has an enthalpy of 410 B.t.u./lb. relative to liquid methane at atmospheric pressure The nitrogen stream 13 withdrawn from first heat exchanger 2 has a temperature of 70 F. and a pressure of 15 p.s.i.'a. and it is passed at a rate of 12.2 lbs/unit time 'to compressor 14 where it is compressed to 50 p.s.i.a. and cooled in cooler 16 to atempe'ratu're of 80 F. Compression of the nitrogen stream by compressor 17 results in an increase in its pressure to 155 p.s.i.a., the cooling 'jby cooler 20 being'ag'ain' to a temperature of '80" F. The resulting compressed cooled stream 18,'at a temperature of 80 F. with an enthalpy of 186 'B.t.u./1b. is divided, the first part 'bein'g passe'd via line '19 at 80 F. to the first heat exchanger 2 and the other part being passed at 1 1b./unit time to expansion means 22, where the temperature drops to 170 F. and the pressure to 15 p;s.i.a. This latter 7,

stream 23 is then passed through heat exchanger zfrom it is passed to the last heat exchanger 4. The cooled re-' 'frigerant stream 33 withdrawn from heat exchanger 3 at -'l46 F is divided, the first part being passed .via line 34-to the heat exchanger 4 and the other part at 1.6 lbs/unit time and an enthalpy of 127 Btu/lb. being passed to expansion means 37. The expanded nitrogen stream 38, having a temperature of 300 F a pressure of 15 p.s.i.a. and having an enthalpy of 92 B.'t.u./lb. is thenpassed through heat exchanger 4, from which it is withdrawn with an enthalpy of 128 Btu/lb. and combined with stream 49 having a temperature -156 F.

The cooled process stream 39 withdrawn from the last heat exchanger 4 in the first plurality of heat exchangers is at its'dew point, '-259 F., and it is liquefied at this temperature by successively passing it through the second plurality of heat exchangers 6, 7 and 8. To accomplish this liquefaction, the cooled refrigerant stream 41 withdrawn from the last heat exchanger 4 in the first group of heat exchangers is passed at 260 F. and 8.4 lb./unit time to expansion means 42, where it is expanded to a pressure of p.s.i.a. and passed via line '43 at 285 F. to the last heat exchanger 8 in the second group of heat exchangers. The refrigerant is withdrawn via line 44 from heat exchanger 8 at --270 F. and expanded by means 46 to 40 p.s.i.a. and -300 F., withdrawn from heat exchanger 7 at -270 F. and expanded by means 48 to 15 p.s.i.a. and 315 F., and thereafter withdrawn from the first heat exchanger 6 in the second group of heat exchangers at a temperature of 270 F. and a pressure of 15 p.s.i.a., this stream then being passed to the lastheat exchanger 4 of the first group of heat exchangers. Product (liquid methane) is passed via line 9 to storage vessel 11 at -259 F. and 15 p.slia. The power consumption of the above-described example on the production basis of 100,000,000 lbs/stream day of liquid methane requires 140,000 horsepower.

Although this invention is especially adapted to the liquefaction of methane with nitrogen as the refrigerant (or helium), the invention is broadly applicable to lowering the temperature of any material with or without a phase change in such material. Other low boiling gases (-i.e., those boiling below F.) includes natural gas, ethane, ethylene, acetylene, carbon monoxide, carbon dioxide,- air, hydrogen, oxygen, nitrogen, and the like. These materials can be used as refrigerants for one another, the criterion being that the gas used as refrigerant have a boiling point lower than that of the gas being liquefied. It is also possible, according to this invention, to freeze (solidify) a liquid by first removing its sensible heat and then removing its latent heat of fusion, 'to sublime a gas by removing its heat of sublimation. Also, it is possible, according to this invention, to remove only part or all of the sensible heat of a material and not cause the latter to go through a phase change, as would bethecase where one is interested in maintaining a solid at a low temperature, such as foodstuffs to preserve the same and prevent bacterial degradationthereof.

new 1 Tim Various modifications and alterations of this invention will become apparent to those skilled in the art from the foregoing discussion and accompanying drawing without departing from the scope and spirit of thi invention, and it should be understood that this invention is not to be limited unduly to that set forth herein for illustrative purposes.

I claim:

1. A process for liquefying a gas, which process comprises: successively passing a process stream (1) of said gas through a plurality of first indirect heat exchange zones and thence through a plurality of second indirect heat exchange zones at a constant pressure; successively passing a compressed stream (2) of gaseous refrigerant through said first heat exchange zones in concurrent flow to said process stream 1); successively passing an expanded stream (3) of said refrigerant through said first heat exchange zones in countercurrent flow .to said process stream (1); for each of said first heat exchange zones, passing a stream (4) of said refrigerant therethrough in countercurrent flow to said process stream (1), said stream (4) being obtained from said stream (2) at a point immediately upstream of the latter zone, expanded upstream of the latter, and combined with said stream (3) immediately downstream of the latter zone; compressing and cooling the combined streams (3) and (4) withdrawn from the first of said first heat exchange zones to provide said stream (2); expanding said stream (2) Withdrawn from the last of said first heat exchange zones and successively passing the resulting expanded .stream through said second heat exchange zones from the last to the first thereof in countercurrent flow to said process stream (1) with expansion of the latter expanded stream between each of said second heat exchange zones; employing the latter stream withdrawn from the first of said second heat exchange zones as said stream (3); and withdrawing all of said process stream (1) from the last of said second heat exchange zones as liquefied product.

2. The process according to claim 1, wherein said process stream is methane.

3. The process according to claim 2, wherein said gaseous refrigerant is nitrogen.

4. Apparatus for liquefying a gas, comprising, in combination: a plurality of first indirect heat exchange means; a plurality of second indirect heat exchange means; first conduit means for successively passing a process stream 1) of said gas through said first heat exchange means and thence through said second heat exchange means at constant pressure; second conduit means for successively passing a compressed stream (2) of gaseous refrigerant through said first heat exchange means in concurrent flow with said process stream (1); third conduit means for successively passing an expanded stream (3) of said gaseous refrigerant through said first heat exchange means in countercurrent flow to said process stream (1); a plurality of fourth conduit means each of which is associated with a different one of said first heat exchange means for passing therethrough an expanded stream (4) of said gaseous refrigerant in countercurrent fiow to said process stream (1), each of said fourth conduit means associated with said one first heat exchange means being connected at its upstream end with said second conduit means at a point immediately upstream of where the latter conduit means passes said stream (12) through the latter heat exchange means and being connected at its downstream end with said third conduit means at a point immediately downstream of where the latter conduit means withdraws said stream (3) from the latter heat exchange means; expansion means in each of said fourth conduit means; fifth conduit means connected at one end of said third conduit means at a point downstream of where the latter with draw-s said stream (3) from the first of said first heat exchange means and connected at the other end to said second conduit means at a point upstream of Where the latter is connected to that said fourth conduit means associated with the latter heat exchange means; means in said fifth conduit means for compressing and cooling the combined streams (3) and (4) flowing therethrough; sixth conduit means connected at one end to the downstream end of said second conduit means and at the other end of the upstream end of said third conduit means, said sixth conduit means successively passing said stream (2) of said gaseous refrigerant through said plurality of said second heat exchange means from the last to the first thereof in countercurrent flow to said process stream (1); a plurality of expansion means each of which is disposed in said sixth conduit means at a point upstream of a different one of said second heat exchange means; and seventh conduit means connected to the downstream end of said first conduit means to withdraw all of said process stream (1) from the last of said second heat exchange means as liquid.

References Cited by the Examiner UNITED STATES PATENTS 2,458,894 1/49 Collins 63-8l8 X 2,909,903 10/59 Zimmerman,

FOREIGN PATENTS 3/59 France.

OTHER REFERENCES NORMAN Y'UDKOFF, Primary Examiner. 

1. A PROCESS FOR LIQUEFYING A GAS, WHICH PROCESS COMPRISES: SUCCESSIVELY PASSING A PROCESS STREAM (1) OF SAID GAS THROUGH A PLURALITY OF FIRST INDIRECT HEAT EXCHANGE ZONES AND THENCE THROUGH A PLURALITY OF SECOND INDIRECT HEAT EXCHANGE ZONES AT A CONSTANT PRESSURE; SUCCESSIVELY PASSING A COMPRESSED STREAM (2) OF GASEOUS REFRIGERANT THROUGH SAID FIRST HEAT EXCHANGE ZONES IN CONCURRENT FLOW TO SAID PROCESS STREAM (1); SUCCESSIVELY PASSING AN EXPANDED STREAM (3) OF SAID REFRIGERANT THROUGH SAID FIRST HEAT EXCHANGE ZONES IN COUNTERCURRENT FLOW TO SAID PROCESS STREAM (1); FOR EACH OF SAID FIRST HEAT EXCHANGE ZONES, PASSING A STREAM (4) OF SAID REFRIGERANT THERETHROUGH IN COUNTERCURRENT FLOW TO SAID PROCESS STREAM (1), SAID STREAM (4) BEING OBTAINED FROM SAID STREAM (2) AT A POINT IMMEDIATELY UPSTREAM OF THE LATTER ZONE, EXPANDED UPSTREAM OF THE LATTER, AND COMBINED WITH SAID STREAM (3) IMMEDIATELY DOWNSTREAM OF THE LATTER ZONE; COMPRESSING AND COOLING THE COMBINED STREAMS (3) AND (4) WITHDRAWN FROM THE FIRST OF SAID FIRST HEAT EXCHANGE ZONES TO PROVIDE SAID STREAM (2); EXPANDING SAID STREAM (2) WITHDRAWN FROM THE LAST OF SAID FIRST HEAT EXCHANGE ZONES AND SUCCESSIVELY PASSING THE RESULTING EXPANDED STREAM THROUGH SAID SECOND HEAT EXCHANGE ZONES FROM THE LAST TO THE FIRST THEREOF IN COUNTERCURRENT FLOW TO SAID PROCESS STREAM (1) WITH EXPANSION OF THE LATTER EXPANDED STREAM BETWEEN EACH OF SAID SECOND HEAT EXCHANGE ZONES; EMPLOYING THE LATTER STREAM WITHDRAWN FROM THE FIRST OF SAID SECOND HEAT EXCHANGE ZONES AS SAID STREAM (3); AND WITHDRAWING ALL OF SAID PROCESS STREAM (1) FROM THE LAST OF SAID SECOND HEAT EXCHANGE ZONES AS LIQUEFIED PRODUCT. 